Re: [Crash-utility] [PATCH] x86_64: Make the conversion between 4level and 5level paging automatically
Dear Dave,
At 07/06/2018 09:45 PM, Dave Anderson wrote:
----- Original Message -----
> Currently, Crash only enable support for kernel-only 5-level page tables by
> entering the command line option "--machdep vm=5level". Since Linux 4.17,
> the Linux kernel can be both 4level and 5level page tables. This command line
> can't work well for this.
>
> Using the "pgtable_l5_enabled" got from vmcore to detect whether the
kernel
> proper for 5 level page tables automatically.
Hello Dou,
Presumably by the time arch_crash_save_vmcoreinfo calls pgtable_l5_enabled(),
things have been initialized up appropriately, and so this should work OK for
kdump-generated vmcores. But have you looked into how this should be accomplished
for for live systems? Since kernel commit 51be1335 reverts __pgtable_l5_enabled
I tested in live system, it didn't work, need use the "--machdep
vm=5level" like before.
from being __initdata to __ro_after_init, would it be as simple as
just reading
__pgtable_l5_enabled at POST_RELOC time?
Yes, I agree, but, how can we read the '__pgtable_l5_enabled' in
crash. Is there a ready-made interface such as symbol_value() for SYMBOL
values?
And seems read at POST_RELOC time is late, it should be earlier than
PRE_GDB.
Thanks,
dou.
Thanks,
Dave
> Signed-off-by: Dou Liyang <douly.fnst(a)cn.fujitsu.com>
> ---
> x86_64.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/x86_64.c b/x86_64.c
> index 6d1ae2f..be6164b 100644
> --- a/x86_64.c
> +++ b/x86_64.c
> @@ -203,6 +203,10 @@ x86_64_init(int when)
> machdep->machspec->kernel_image_size = dtol(string, QUIET, NULL);
> free(string);
> }
> + if ((string = pc->read_vmcoreinfo("NUMBER(pgtable_l5_enabled)"))) {
> + machdep->flags |= VM_5LEVEL;
> + free(string);
> + }
> if (SADUMP_DUMPFILE() || QEMU_MEM_DUMP_NO_VMCOREINFO() ||
> VMSS_DUMPFILE())
> /* Need for calculation of kaslr_offset and phys_base */
> --
> 2.14.3
>
>
>
>